Heat treatment system

ABSTRACT

The present invention is a thermal processing unit that includes: a tubular processing container; an object-to-be-processed holding unit that holds a plurality of objects to be processed in a tier-like manner and that can be inserted into and taken out from the processing container; a process-gas introducing unit that introduces a predetermined process gas into the processing container; a heating unit provided in the processing container, the heating unit heating the plurality of objects to be processed held by the object-to-be-processed holding unit when the object-to-be-processed holding unit is inserted into the processing container; and a container cooling unit that cools an outside wall surface of the processing container.

FIELD OF THE INVENTION

This invention relates to a thermal processing unit that conducts apredetermined process to an object to be processed, such as asemiconductor wafer, at a relatively low temperature.

BACKGROUND ART

In general, in order to manufacture a desired semiconductor integratedcircuit, various thermal processes including a film-forming process, anetching process, an oxidation process, a diffusion process, a modifyingprocess or the like are carried out to a semiconductor wafer, whichconsists of a silicon substrate or the like. These thermal processes maybe conducted by a longitudinal batch-type of thermal processing unit. Inthe case, at first, from a cassette that can contain a plurality of, forexample 25 semiconductor wafers, semiconductor wafers are conveyed ontoa longitudinal wafer boat. For example, 30 to 150 wafers (depending onthe wafer size) are placed on the wafer boat in a tier-like manner. Thewafer boat is conveyed (loaded) into a processing container that can beexhausted, through a lower portion thereof. After that, the inside ofthe processing container is maintained at an airtight state. Then,various process conditions including a flow rate of a process gas, aprocess pressure, a process temperature or the like are controlled toconduct a predetermined thermal process.

Herein, with reference to FIG. 10, an example of a conventional thermalprocessing unit is explained. The thermal processing unit 2 has alongitudinal processing container 8 with a predetermined length, whichhas a double-tube structure of an inner tube 4 and an outer tube 6 andis made of quartz. In a processing space S in the inner tube 4, a waferboat 10 made of quartz is contained as a holder for holding the objectto be processed. Semiconductor wafers W as objects to be processed areheld on the wafer boat 10 in a tier-like manner at a predeterminedinterval (pitch).

A cap 12 is provided for opening and closing a lower portion of theprocessing container 8. A rotation shaft 16, which can rotate via amagnetic-fluid seal 14, is provided at the cap 12. A rotation table 18is provided on an upper end of the rotation shaft 16. A heat-insulatingcylinder 20 is provided on the table 18. The wafer boat 10 is placed onthe heat-insulating cylinder 20. The cap 12 is attached to an arm 24 ofa boat elevator 22 that can be moved up and down, so that the cap 12 canbe moved up and down together with the rotation shaft 16 and the waferboat 10 and the like. Because of the up-and-down movement by the boatelevator 22, the wafer boat 10 can be inserted into or taken out fromthe processing container 8 through a bottom portion of the processingcontainer 8.

A manifold 26 made of for example stainless steel is joined to alower-end opening of the processing container 8. A plurality of (two inthe shown example) gas nozzles 28A, 28B penetrates the manifold 26 forintroducing various process gases necessary for a thermal process, forexample a film-forming process, into the processing container 8. Therespective gas nozzles 28A, 28B are connected to respective gassupplying systems 30A, 30B. In the respective gas supplying systems 30A,30B, flow-rate controllers 32A, 32B such as mass-flow controllers thatcan control gas flow rates are respectively provided.

Then, the respective process gases supplied from the respective gasnozzles 28A, 28B ascend in the processing space S (wafer containingregion) in the inner tube 4, turn down at a ceiling portion and descendin a gap between the inner tube 4 and the outer tube 6.

A gas-discharging port 34 communicating with the gap between the innertube 4 and the outer tube 6 is provided at a side wall of the manifold26. A vacuum pump not shown and the like are connected to thegas-discharging port 34. Thus, a vacuum can be created in the processingcontainer 8.

A heat-insulating barrier 36 consisting of a heat-insulating material isprovided outside the processing container 8. A heater 38 as a heatingmeans is provided inside the heat-insulating barrier 36. Thus, thewafers W in the processing container 8 are adapted to be heated to apredetermined temperature.

The conventional thermal processing unit 2 is designed to conduct athermal process, such as a film-forming process or anoxidation-diffusion process, at a relatively high temperature zone offor example 900 to 1200° C. In view of thermal stability at therelatively high temperature zone and so on, the heat-insulating barrier36 is designed to be relatively thick so as to have large thermalcapacity. In addition, in order to rapidly lower the temperature of theprocessed wafers, a thermal processing unit has been proposed wherein acool wind is blown to an outside surface of the processing container(for example, JP laid-Open Publication No. 2000-100812).

Recently, it is possible that the semiconductor wafers have to bethermally processed at a relatively low temperature zone of for example50 to 600° C., instead of the relatively high temperature zone of forexample 900 to 1200° C. For example, in order to grant a request ofhigh-speed operation of a semiconductor device, if copper wiring thathas been recently paid attention to is formed to reduce wiringresistance, it may be necessary to conduct an annealing process tocopper films coated on the wafers at a relatively low temperature ofabout 50 to 150° C. In addition, in order to reduce wiring capacity, ifan organic film whose dielectric constant is small, such as a resin, isused as an interlayer dielectric film, it may be necessary to vitrifythe organic film at a relatively low temperature of about 400 to 600° C.

When a thermal process is conducted at the above low temperature zone,if the thermal processing unit 2 as shown in FIG. 6, which is designedfor the high temperature zone of for example 900 to 1200° C. and whichhas the large thermal capacity, is used, it may take a very long time tolower the wafer temperature to a handling temperature that is around aroom temperature, even if the thermal process is conducted at the lowtemperature. For example, as described above, since the heat-insulatingbarrier 36 is thick and has the large thermal capacity, a rate oftemperature fall in the high-temperature zone of about 900 to 1200° C.is 5 to 6° C./min, which is large, but a rate of temperature fall in thelow temperature zone of around 100° C. is 1 to 2° C./min, which is verysmall. The phenomenon in the low temperature zone may be also found inanother unit wherein a cooling wind is blown to a side wall of aprocessing container 8.

If it takes a long time to lower the temperature of the processed wafersto the handling temperature, throughput is remarkably deteriorated.

SUMMARY OF THE INVENTION

This invention is intended to solve the above problems. The object ofthis invention is to provide a thermal processing unit wherein a rate oftemperature fall in a low-temperature zone of for example 50 to 600° C.is high and wherein throughput of a thermal process is improved.

This invention is a thermal processing unit comprising: a tubularprocessing container; an object-to-be-processed holding unit that holdsa plurality of objects to be processed in a tier-like manner and thatcan be inserted into and taken out from the processing container; aprocess-gas introducing unit that introduces a predetermined process gasinto the processing container; a heating unit provided in the processingcontainer, the heating unit heating the plurality of objects to beprocessed held by the object-to-be-processed holding unit when theobject-to-be-processed holding unit is inserted into the processingcontainer; and a container cooling unit that cools an outside wallsurface of the processing container.

According to the invention, since the heating unit is provided in theprocessing container and the outside wall surface of the processingcontainer is cooled by the container cooling unit, the whole thermalprocessing unit has smaller thermal capacity. In addition, since theoutside wall surface of the processing container can be maintained at alow temperature, a rate of temperature fall of the objects to beprocessed in a low temperature zone can be remarkably enhanced.

For example, the container cooling unit has: a cooling pipe arranged soas to come in contact with the outside wall surface of the processingcontainer, and a cooling-medium introducing unit that causes a coolingmedium to flow into the cooling pipe. In the case, the outside wallsurface of the processing container can be efficiently cooled by thecooling medium. In addition, it is preferable that the cooling pipe iswound around the outside wall surface of the processing container.

The cooling pipe may have a double-tube structure having an inner tubeand an outer tube, and the cooling medium may be caused to flow into agap between the inner tube and the outer tube.

In addition, it is preferable that the outside wall surface of theprocessing container and the cooling pipe are coated with aheat-transfer material. In the case, the heating surface area can beincreased, the heat exchange effectiveness can be improved, and the rateof temperature fall can be also improved.

For example, the heat-transfer material is a heat-transfer cement.

In addition, preferably, provided is a cooling-gas introducing unit thatintroduces a predetermined cooling gas into the processing containerwhen the objects to be processed are cooled. In the case, since thecooling gas can be directly introduced into the processing container bythe cooling-gas introducing unit, the rate of temperature fall andcharacteristics of temperature fall in a low temperature zone can bemore improved.

In addition, preferably, a thermal-reflectivity lowering process forlowering thermal reflectivity of an inside wall surface of theprocessing container may have been conducted to the inside wall surfaceof the processing container. In the case, since the thermal reflectivityof the inside wall surface of the processing container is lowered, heatin the processing container can be absorbed by the inside wall surfaceand efficiently discharged outside by the container cooling unit. Thus,cooling efficiency can be improved, so that the rate of temperature falland the characteristics of temperature fall can be more improved.

For example, the heating unit has a side heater extending in a verticaldirection along the inside wall surface of the processing container.Regarding support of the side heater, although a lower portion of theside heater may supported by a bottom portion of the processingcontainer, it is preferable that a upper portion of the side heater issupported by a ceiling portion of the processing container. This isbecause the ceiling portion of the processing container has relativelylarge space. In addition, this makes it possible to avoid concentrationof pipes or the like at the lower portion of the processing container inwhich the pipes or the like, such as the process-gas introducing unitand the cooling-gas introducing unit, tend to be concentratedlyarranged. In the case, maintenance characteristics at the lower portionof the processing container may be improved.

Preferably, the heating unit has a ceiling heater arranged in a vicinityof a ceiling portion of the object-to-be-processed holding unit insertedinto the processing container, the ceiling heater heating the ceilingportion. Similarly, preferably, the heating unit has a bottom heaterarranged in a vicinity of a bottom portion of the object-to-be-processedholding unit inserted into the processing container, the bottom heaterheating the bottom portion.

In the case, more quantity of heat can be given to the objects to beprocessed held at the ceiling portion (upper portion) and the bottomportion (lower portion) of the object-to-be-processed holding unit,whose heat discharge tends to be larger than at the central portion.Thus, high temperature-control characteristics can be maintained andtemperature uniformity between surfaces of the objects to be processedcan be improved.

It is preferable that the ceiling heater is supported by a ceilingportion of the processing container. Similarly, it is preferable thatthe bottom heater (assistant bottom heater) is also supported by aceiling portion of the processing container. Alternatively, if theprocessing container has a lower-end opening and the lower-end openingcan be opened and closed by a lid member, the bottom heater may besupported by the lid member.

The processing container consists of quartz, stainless steel oraluminum.

Preferably, the objects to be processed are heated to a range of 50 to600° C.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic structural view showing a first embodiment of athermal processing unit according to the present invention;

FIG. 2 is a sectional view of the thermal processing unit of theembodiment;

FIG. 3 is a perspective view of a heater rod as a heating unit;

FIGS. 4(A) and 4(B) are graphs showing examples of characteristics oftemperature fall of wafers according to the thermal processing unit ofthe first embodiment of the present invention;

FIG. 5 is a graph showing wafer temperatures when the wafers are heated;

FIG. 6 is a schematic structural view showing a second embodiment of athermal processing unit according to the present invention;

FIGS. 7(A) and 7(B) are plan view showing examples of a shape of aceiling heater or a bottom heater;

FIG. 8 is a graph showing characteristics of temperature rise of wafersaccording to a conventional unit;

FIG. 9 is a graph showing characteristics of temperature rise of wafersaccording to the thermal processing unit of the second embodiment of thepresent invention; and

FIG. 10 is a schematic structural view showing an example of aconventional thermal processing unit.

DESCRIPTION OF THE PREFERRED EMBODIMENT

Hereinafter, embodiments of a thermal processing unit according to thepresent invention are explained with reference to attached drawings.

FIG. 1 is a schematic structural view showing a first embodiment of athermal processing unit according to the present invention. FIG. 2 is asectional view of the thermal processing unit of the embodiment.

FIG. 3 is a perspective view of a heater rod as a heating unit.

As shown in FIG. 1, a thermal processing unit 40 of the first embodimentof the invention has a cylindrical processing container 42 whose lowerend is open. The processing container 42 may be made of for examplequartz or a metal such as stainless steel or aluminum. In a lowtemperature zone of about 50 to 600° C. as described above, if a processof semiconductor wafers is conducted mainly in a higher zone of about350 to 600° C., it is preferable that quartz, whose heat resistance ishigh, is used as a material for the processing container 42. If aprocess of semiconductor wafers is conducted mainly in a lower zone ofabout 50 to 350° C., it is preferable that a metal such as stainlesssteel or aluminum is used as a material for the processing container 42.

An open gas-discharging port 46 is provided at a ceiling part of theprocessing container 42. A gas-discharging nozzle 48 that has been bentat a right angle in a lateral direction is provided to connect with thegas-discharging port 46. A gas-discharging system 54 including apressure-control valve 50 and a gas-discharging pump 52 and the like onthe way is connected to the gas-discharging nozzle 48. Thus, theatmospheric gas in the processing container 42 can be discharged.Herein, the inside of the processing container 42 may be a vacuum or asubstantially normal-pressure atmosphere, depending on a process manner.

A lower end of the processing container 42 is supported by a cylindricalmanifold 56 made of for example stainless steel. Under the manifold 56,a wafer boat 58 made of quartz as an object-to-be-processed holdingunit, on which a large number of semiconductor wafers W as objects to beprocessed are placed in a tier-like manner, is provided in a verticallymovable manner.

The wafer boat 58 can be inserted into and taken out from the processingcontainer 42, through a lower opening of the manifold 56. In theembodiment, for example about 30 wafers W having 300 mm diameter may besupported in a tier-like manner at substantially the same interval(pitch) by the wafer boat 58. A sealing member 57 such as an O-ring isinterposed between a lower end of the processing container 42 and anupper end of the manifold 56. Thus, airtightness between the processingcontainer 42 and the manifold 56 is maintained.

The wafer boat 58 is placed above a table 62 via a heat-insulatingcylinder 60 made of quartz. The table 62 is supported on a rotationshaft 66 that penetrates a lid member 64 for opening and closing thelower end opening of the manifold 56.

For example, a magnetic-fluid seal 68 is provided at a penetration partof the lid member 64 by the rotation shaft 66. Thus, the rotation shaft66 can rotate while maintaining airtightness by the lid member 64. Inaddition, a sealing member 70 such as an O-ring is provided between aperipheral portion of the lid member 64 and a lower end portion of themanifold 56. Thus, airtightness between the lid member 64 and themanifold 56 is maintained, so that airtightness in the processingcontainer 42 is maintained.

The rotation shaft 66 is attached to a tip end of an arm 74 supported byan elevating mechanism 72 such as a boat elevator. When the elevatingmechanism 72 is moved up and down, the wafer boat 58 and the lid member64 and the like may be integrally moved up and down.

Herein, the table 62 may be fixed on the lid member 64. In the case, thewafer boat 58 doesn't rotate while the process to the wafers W isconducted.

A heating unit 76 for heating the semiconductor wafers W, a process-gasintroducing unit 78 for introducing a predetermined process gas into theprocessing container 42, and a cooling-gas introducing unit 80 as onefeature of the present invention are respectively provided at a sideportion of the manifold 56.

Specifically, for example as shown in FIG. 3, the heating unit 76 has along heater rod 82 that extends vertically and whose upper portion isbent in a U-shape. As shown in FIGS. 1 and 2, a plurality of heater rods82, eight heater rods 82 in the case shown in FIG. 2, are providedsubstantially uniformly in a circumferential direction of the processingcontainer 42. Of course, the number of heater rods is not limited. Thelength of the heater rod 82 is greater than height of the wafer boat 58.Each heater rod 82 is arranged along an inside wall surface of theprocessing container 42 and away from the inside wall surface by aslight distance. A lower end portion 82A of the heater rod 82 is bent ata substantially right angle in a L-shape. The lower end portion 82A isfixed to the manifold 56. Thus, the whole heater rod 82 is supported.

For example, a carbon wire heater wherein a carbon wire is covered witha quartz layer can be used as the heater rod 82. Each heater rod 82 isconnected to a heater electric power source 86 via a feeder line 83 anda switching mechanism 84.

The process-gas introducing unit 78 has a plurality of, two in the shownexample, process-gas nozzles 88A, 88B that penetrate the manifold 56.The process-gas nozzles 88A, 88B are respectively connected toprocess-gas sources 92A, 92B via process-gas lines 90A, 90B. In therespective process-gas lines 90A, 90B, on-off valves 94A, 94B andflow-rate controllers 96A, 96B such as mass-flow controllers arerespectively provided. Necessary numbers of the process-gas nozzles 88A,88B and the like are provided depending on the number of kinds ofnecessary gases. The tip end portion of each process-gas nozzle 88A, 88b is bent upwardly.

In addition, as shown in FIGS. 1 and 2, the cooling-gas introducing unit80 has a plurality of, eight in the shown example, cooling-gas nozzles98 that penetrate the manifold 56. These gas nozzles 98 are arrangedsubstantially uniformly (at substantially the same pitch) in acircumferential direction of the manifold 56. The tip end portion ofeach cooling-gas nozzle 98 is bent upwardly. Each cooling-gas nozzle 98is connected to a cooling-gas source 104 via a cooling-gas line 100including an on-off valve 102 on the way. As described below, a coolinggas is adapted to be ejected from each cooling-gas nozzle 98 into theprocessing container 42 in order to lower the temperature of the wafersafter the thermal process.

As the cooling gas, an inert gas such as an N₂ gas, an Ar gas or a Hegas, or a clean air or the like may be used. In addition, if a coolingmechanism not shown is provided in the cooling-gas line 100 to cool thecooling gas to a lower temperature before ejection of the cooling gas, arate of temperature fall of the wafers can be more enhanced.

In addition, a container cooling unit 110 for cooling the processingcontainer 42 itself is provided at the processing container 42.Specifically, the container cooling unit 110 of the embodiment has acooling pipe 112 closely and for example spirally wound around anoutside wall surface of the processing container 42. The cooling pipe112 is made of a material whose heat conductivity is good, such ascopper, and is wound over substantially the whole height of theprocessing container 42.

One end of the cooling pipe 112 is formed as a cooling-mediumintroducing port 112A, and the other end is formed as a cooling-mediumdischarging port 112B. Then, the cooling-medium introducing port 112A isconnected to a cooling-medium source 114 via a cooling-medium way 118including an on-off valve 116 on the way. For example, cooling water maybe used as the cooling medium. However, the cooling medium is notlimited thereto. It is preferable that the cooling medium is repeatedlyused by means of a circulation way.

In the present embodiment, a heat-transfer cement 120 whose heatconductivity is good and that has a predetermined thickness is attachedonto the outside wall surface of the processing container 42 in such amanner that the cooling pipe 112 is buried in the-heat-transfer cement120. Thus, the side wall of the processing container 42 can be moreefficiently cooled when necessary.

Next, a thermal processing method carried out by using the thermalprocessing unit of the embodiment as described above is explained.Herein, as a thermal process, an annealing process for copper filmsformed on wafer surfaces is explained as an example.

When the semiconductor wafers W are unloaded and the thermal processingunit is under a waiting state, the processing container 42 is maintainedat a temperature, for example about 50° C., which is lower than aprocess temperature. Then, the wafer boat 58 on which a large number of,for example thirty, wafers W at a normal temperature are placed is movedup and loaded into the processing container 42 from the lower portionthereof. The lid member 64 closes the lower end opening of the manifold56, so that the inside of the processing container 42 is hermeticallysealed.

Then, the inside of the processing container 42 is vacuumed andmaintained at a predetermined process pressure, for example about 100Pa. On the other hand, electric power supplied to the heater rods 82 ofthe heating unit 76 is increased so that the wafer temperature is raisedand stabilized at a process temperature for the annealing process, forexample about 150° C. After that, an H₂ gas as a predetermined processgas is supplied from one process-gas nozzle (for example 88A) of theprocess-gas introducing unit 78 while a flow rate of the H₂ gas iscontrolled.

The H₂ gas ascends in the processing container 42 and comes in contactwith the wafers W contained in the rotating wafer boat 58. Thus, theannealing process is conducted to the copper films of the wafersurfaces. Then, the H₂ gas is discharged outside from thegas-discharging port 46 at the ceiling part of the processing container42.

During the thermal process (annealing process), a cooling medium such ascooling water may be caused to flow into the cooling pipe 112 of thecontainer cooling unit 110 provided on the side wall of the processingcontainer 42. In the case, the side wall of the container may be cooled.If the cooling medium such as cooling water is not caused to flow, thethermal efficiency of the process may be enhanced.

When the thermal process for a predetermined time is completed, theelectric power supplied to the heater rods 82 is controlled or stopped.Then, a cooling operation is conducted.

The cooling medium continues to be caused to flow into the cooling pipe112 of the container cooling unit 110 (if the cooling medium has notbeen caused to flow during the thermal process, the cooling mediumstarts to be caused to flow), so that the side wall of the processingcontainer 42 continues to be cooled.

The supply of the process gas from the process-gas nozzle 88A of theprocess-gas introducing unit 78 is stopped. On the other hand, from eachcooling-gas nozzle 98 of the cooling-gas introducing unit 80, thecooling gas (for example, an N₂ gas or a clean air) is ejected into theprocessing container 42. Thus, the cooling of the wafers W is promoted.

As described above, the side wall of the processing container 42 isdirectly cooled by causing the cooling water or the like to flow intothe cooling pipe 112, and the thermal capacity of the whole heatingfurnace including the processing container 42 and the heat-transfercement 120 and the like is small. Thus, the wafers W may be efficientlycooled, that is, the rate of temperature fall of the wafers W may beincreased.

In the present embodiment, the cooling pipe 112 is buried in theheat-transfer cement 120, so that the thermal conductivity between theside wall of the processing container 42 and the cooling pipe 112 isgreatly increased. Thus, the temperature of the processing container 42may be lowered more rapidly.

In addition, at the same time as the cooling by the cooling pipe 112,the cooling gas is introduced into the processing container 42 from thelower portion thereof, and the cooling gas directly contacts with theprocessed wafers W to cool them. Thus, the temperature of the wafers Wmay be lowered more rapidly, that is, the rate of temperature fall ofthe wafers W may be increased more.

In addition, if a thermal-reflectivity lowering process for loweringthermal reflectivity of the inside wall surface of the processingcontainer 42 has been conducted to the inside wall surface of theprocessing container 42 in advance, heat absorptivity of the side wallof the processing container 42 is increased. In the case, thetemperature in the processing container 42 and the temperature of thewafers W may be lowered more rapidly. As a thermal-reflectivity loweringprocess, there are a blacking process to the inside wall surface of thecontainer, a process of making rough the inside wall surface of thecontainer by sandblasting or the like, and the like.

A metal tube having a double-tube structure may be used as the containercooling unit 110, and a cooling medium may be caused to flow between thedouble tubes.

Although the heater rods 82 are provided in the processing container 42,there is no fear that the wafers are metal contaminated because theprocess temperature is low, the process is the annealing process for thecopper films, and the surfaces of the heater rods 82 are covered withthe quartz and the like.

Herein, an evaluation test was actually conducted regarding when thewafers are cooled in the above thermal processing unit 40. Theevaluation result is explained.

FIG. 4 is graphs showing characteristics of temperature fall of thesemiconductor wafers. FIG. 4(A) shows characteristics of temperaturefall when the cooling water flows into the cooling pipe but the coolinggas is not ejected. FIG. 4(B) shows characteristics of temperature fallwhen the cooling water flows into the cooling pipe and the cooling gasis ejected into the processing container. Herein, the showncharacteristics are those when the wafer temperature is lowered fromabout 150° C. to a room temperature. The flow rate of the cooling waterwas 5 liters/min, the cooling gas was a clean air, and the flow rate ofthe cooling gas was 666 liters/min, in common.

As shown in FIG. 4(A), when the cooling gas was not ejected and only thecooling water was used, the temperature fall traced a relatively mildcurve. However, in the higher temperature zone, the rate of temperaturefall was higher than in the lower temperature zone. For example, from150° C. to 100° C., the rate of temperature fall was 5.9° C./min, whilefrom 150° C. to 50° C. the rate of temperature fall was 4.3° C./min. Therate of temperature fall of the case is much higher than the rate oftemperature fall of 1 to 2° C./min at the conventional thermalprocessing unit shown in FIG. 6. That is, it was found that an enoughhigh rate of temperature fall can be obtained even if the cooling gas isnot used.

On the other hand, as shown in FIG. 4(B), when both the cooling gas andthe cooling medium were used, the temperature fall traced a relativelysharp curve. That is, the degree of temperature fall was very great. Forexample, from 150° C. to 100° C., the rate of temperature fall was 15.2°C./min, while from 150° C. to 50° C. the rate of temperature fall was11.1° C./min. In the case, it was found that a very high rate oftemperature fall can be obtained even compared with the case shown inFIG. 4(A).

Thus, the unit 40 of the present embodiment can lower the temperature ofthe processed wafers more rapidly; thereby the throughput may beremarkably improved.

In addition, an evaluation test was conducted regarding a heatingoperation of the wafer temperature at a start of the thermal process tothe wafers. The evaluation result is explained. FIG. 5 is a graphshowing an evaluation result when the wafer temperature is raised. InFIG. 5, a line A shows a set value from a computer of a temperaturecontrolling system, a curve B shows electric power supplied to theheater rods 82, and a curve C shows the wafer temperature. The settemperature was 150° C., and the flow rate of the cooling water was 5liters/min.

According to the curve C in the graph, within about three minutes fromthe start of heating (shorter than a target value, 10 minutes), thewafer temperature reached a temperature in the vicinity (not less than90%) of the set temperature of 150° C. That is, it was found that therate of temperature rise is also high enough and is maintained atsubstantially the same value as at the conventional unit.

Next, a second embodiment of the present invention is explained.

FIG. 6 is a schematic structural view showing the second embodiment of athermal processing unit according to the present invention. FIGS. 7(A)and 7(B) are plan view showing shapes of a ceiling heater and a bottomheater. The same parts as explained with reference to FIG. 1 arerepresented by the same numeral signs, and the explanation thereof isomitted.

In the second embodiment, a material for the processing container 42 islimited to a metal, so that a time necessary for temperaturestabilization is shortened. In addition, the number of heaters in theheating unit 76 is increased, so that the uniformity between wafersurface temperatures during the process is improved.

That is, the processing container 42 of the embodiment is made of ametal material that doesn't cause metal contamination, such as stainlesssteel or anodized aluminum. The ceiling part 42A of the processingcontainer 42 and the lid member 42B for opening and closing the lowerend opening of the processing container 42 are also made of the samemetal material. Then, the height and the diameter of the processingcontainer 42 are respectively about 900 mm and about 500 mm. Thus, thevolume of the processing container 42 is about 173 liters.

In addition, the rotation table 62 for supporting the wafer boat 58 andan upper portion of the rotation shaft 66 connected to the rotationtable 62 are made of a heat-resistant material whose thermalconductivity is low, such as quartz. For example, wafers W of 300 mmdiameter are supported by the wafer boat 58. In the present embodiment,the heat-insulating cylinder 60 (see FIG. 1) used in the firstembodiment shown in FIG. 1 is not used.

As the heating unit 76 of the present embodiment, as described below, aplurality of kinds of heaters are used. In FIG. 6, heating areas of theheaters are shown by dots.

The heaters of the present embodiment are explained in detail.

At first, the same heater rods 82 as shown in FIG. 3 are verticallyarranged along the inside wall surface of the processing container 42.In the same manner as explained with reference to FIG. 2, a large numberof heater rods 82 are arranged at a predetermined interval in acircumferential direction of the processing container 42, in order toform a side heater 130. This feature is the same as the first embodimentexplained with reference to FIG. 1. However, in the present invention,the heater rods 82 are not supported by the side wall of the bottomportion of the processing container 42, but supported by the ceilingportion 42A of the processing container 42.

In addition, in the present embodiment, a bottom heater 132 is arrangedat a bottom portion of the processing container 42 and a ceiling heater134 is arranged at a ceiling portion thereof.

The bottom heater 132 is arranged under the rotation table 62 in such amanner that the bottom heater 132 confronts the rotation table 62 inparallel. Thus, a large amount of heat can be given to the lowermostwafer W, among the wafers W contained in the wafer boat 58 in atier-like manner.

In addition, the ceiling heater 134 is arranged to confront an upper endsurface of the wafer boat 58 in parallel. Thus, a large amount of heatcan be given to the uppermost wafer W, among the wafers W contained inthe wafer boat 58 in a tier-like manner.

The bottom heater 132 is supported by and fixed to the lid member 42Bvia a pillar 136 including a cable, and is connected to the heaterelectric power source 86 (see FIG. 1). On the other hand, the ceilingheater 134 is supported by and fixed to the ceiling portion 42A of theprocessing container 42 via a pillar 138 including a cable, and isconnected to the heater electric power source 86.

As the bottom heater 132 or the ceiling heater 134, as shown in FIG.7(A), a doughnut-like plane heater plate may be used. Alternatively, asshown in FIG. 7(B), the bottom heater 132 or the ceiling heater 134 mayconsist of a plurality of (three in the case of FIG. 7(B)) wire-carbonheater elements, each of which is meanderingly bent in a plane.

Regarding the heater 132 or 134, in order not to cause metalcontamination to the wafers W, the surface thereof may be coated withhigh-purity quartz or the main heater body thereof may be contained in aquartz tube.

In addition, as the bottom heater 132, a heater may be used wherein aresistance heating wire consisting of a high-purity carbon material issealed in a quartz plate, which is described in JP Laid-Open PublicationNo. 2001-156005. The bottom heater 132 may be formed integrally with therotation table 62.

If the above bottom heater 132 and/or the ceiling heater 134 areprovided, a larger amount of heat can be given to the bottom portionand/or the upper portion of the wafer boat 58, whose heat dischargetends to be larger than at the central portion thereof. Thus, theuniformity between surface temperatures of the (for example, abouttwenty-five) wafers W placed on the wafer boat 58 in a tier-like mannercan be maintained at a high level.

If the amount of heat to be given is not enough even with the abovebottom heater 132 and/or the ceiling heater 134, an assistant bottomheater 140 and/or an assistant ceiling heater 142 may be additionallyprovided. The assistant bottom heater 140 and the assistant ceilingheater 142 may be fixed by using an upper space of the processingcontainer 42 that has a running room. That is, the upper end portions ofthe heaters 140 and 142 may be supported by the container ceilingportion 42A. More specifically, a heating area of the assistant bottomheater 140 may be arranged along the inside wall surface of a lowerportion of the processing container 42, and a heating area of theassistant ceiling heater 142 may be arranged along the inside wallsurface of an upper portion of the processing container 42. Thus, thewafers W in the vicinity of the lower end and the wafers W in thevicinity of the upper end may be respectively heated more strongly.

The assistant bottom heater 140 and the assistant ceiling heater 142have the heating areas shown by dots, as described above. The otherconducting portions have small resistance. (For example, the diameter isenlarged to reduce the resistance.) Thus, the other conducting portionsgenerate no heat. Regarding the assistant bottom heater 140 and/or theassistant ceiling heater 142, in order not to cause metal contaminationto the wafers W, it is preferable that the whole heater is coated with aquartz cover or the like.

In addition, a thermal-reflectivity lowering process may be conducted tothe inside wall surface of the processing container 42. Alternatively,without conducting the thermal-reflectivity lowering process, to thecontrary, a thermal-reflectivity raising process may be conducted by anelectro polishing or a chromium plating or the like. For example, if theprocess temperature is in a very low temperature zone of about 50 to400° C. and the control for temperature stabilization is very difficult,it is effective to conduct the thermal-reflectivity lowering process tofacilitate the control for temperature stabilization but to sacrificethe thermal efficiency. To the contrary, if the process temperature isin a normal low temperature zone of about 400 to 600° C., since thecontrol for temperature stabilization is easy, it is effective toconduct the thermal-reflectivity raising process to improve the thermalefficiency.

Then, an operation of the thermal processing unit of the secondembodiment is explained.

The basic operation of the thermal processing unit of the embodiment issubstantially the same as that of the first embodiment. According to thesecond embodiment, since the number of heaters of the heating unit 76 islarge, a higher rate of temperature rise may be achieved. For example,under current operating conditions, a rate of temperature rise of 200°C./min may be obtained at most. If the supplied electric power isreduced, the lower limit of a rate of temperature rise may be reduced toa required small value.

In the thermal processing unit of the second embodiment, for examplewhen the wafer boat 58 is both moved down (unloaded state) and moved upinto the processing container 42 (loaded state), the cooling water isalways caused to flow into the cooling pipe 112, so that the processingcontainer 42 may be cooled to a room temperature. In addition, when thewafer boat 58 holding for example twenty-five wafers W is moved up andloaded into the processing container 42, electric power starts to besupplied at a full power to all the heaters of the heating units 76 thathave been turned off until then, that is, the side heater 130, thebottom heater 132 and the ceiling heater 134, and the assistant bottomheater 140 and the assistant ceiling heater 142 if they are provided.Thus, the wafers W are heated to the process temperature.

In a general processing system wherein the processing container is notcooled, the wafer temperature overshoots so greatly that it takes a longtime for the wafer temperature to stabilize at a process temperature. Onthe other hand, according to the embodiment, since the processingcontainer 42 is cooled, the responsibility of the temperature control isso good that the level of overshooting is inhibited. Thus, it ispossible to stabilize the wafer temperature at a process temperaturewithin a shorter time.

In addition, in the embodiment, by providing the bottom heater 132 andthe ceiling heater 134, and by providing the assistant bottom heater 140and the assistant ceiling heater 142 if they are necessary, an amount ofheat supplied to the upper end portion and the lower end portion of thewafer boat 58, where an amount of heat discharge tends to be larger thanat the central portion thereof, is increased. Thus, the uniformitybetween wafer surface temperatures during the heating step and duringthe process may be enhanced. Thus, it is possible to make substantiallyeven thermal history of all the wafers W placed on the wafer boat 58.

When the process is completed, the electric power supplied to all theheaters 132, 134, 140 and 142 is stopped. The feature wherein thecooling gas such as an N₂ gas is ejected from the cooling-gas nozzle 98is the same as the first embodiment.

Herein, an evaluation test was conducted regarding when the temperatureis raised in the thermal processing unit of the second embodiment. Theevaluation result is explained.

In the thermal processing unit of the present embodiment used for theevaluation test, as the heating unit 176, the side heater 130, thebottom heater 132, the ceiling heater 134 and the assistant bottomheater 140 were provided, but the assistant ceiling heater 142 was notprovided. In addition, a thermal-reflectivity lowering process has beenconducted to the inside wall surface of the processing container 42.

FIG. 8 is a graph showing characteristics of temperature rise of wafersaccording to a conventional unit. FIG. 9 is a graph showingcharacteristics of temperature rise of wafers according to the thermalprocessing unit of the present embodiment. The set temperature was 150°C. for the conventional unit and 100° C. for the embodiment unit. (Sincethe conventional unit is not taken into consideration the use for aprocess at a very low temperature of about 100° C., as the settemperature, 150° C. was adopted, which is a lower limit controllable bythe conventional unit.) In addition, the wafer size was 200 mm (8inches) for the conventional unit and 300 mm (12 inches) for theembodiment unit. The conventional unit contained one hundred and fortywafers, and the embodiment unit contained twenty-five wafers.

Regarding the conventional unit, thermocouples were respectivelyprovided at the fourth uppermost wafer as TOP, at the 70-th uppermostwafer as CENTER and at the 136-th uppermost wafer as BOTTOM, to measuretemperatures thereof. On the other hand, regarding the embodiment unit,thermocouples were respectively provided at the uppermost wafer, at theseventh uppermost wafer, at the sixteenth uppermost wafer and at the25-th uppermost wafer, to measure temperatures thereof. Thethermocouples were provided at a central portion and a peripheralportion for each of the above wafers to measure the temperaturedifference between the central portion and the peripheral portion.

Herein, in the embodiment unit, the process pressure was a normalpressure, the flow rate of the cooling water was 20 liters/min, and theflow rate of the N₂ gas at the cooling step was 5 liters/min.

As shown in FIG. 8, according to the conventional unit, from the startof heating, it took 53 minutes for the wafer temperature to enter arange of 150° C. ±5° C. This time may remarkably deteriorate thethroughput. In addition, during the heating step, the maximumtemperature difference between the wafer surfaces was 30° C., and thestate continued for a long time of about 20 to 30 minutes. That is, itwas found that the thermal history of the wafers may be different to agreat extent. Herein, the wafers were loaded under a condition whereinthe processing container 42 was maintained at 150° C.

On the other hand, as shown in FIG. 9, according to the embodiment unit,from the start of heating, it took only about 7 minutes for the wafertemperature to enter a range of 100° C. ±5° C. In addition, from thecompletion of heating instructions, it took only about 5 minutes for thewafer temperature to enter the temperature stabilization zone. That is,it was found that it is possible to rapidly heat the wafers to apredetermined process temperature. Herein, the rate of temperature risewas 50° C./min.

The reason why the process temperature is stabilized within only about 5minutes from the completion of heating instructions in the embodimentunit is because the wall surface of the processing container 42 iscooled by the cooling water during the heating step so that the degreeof overshooting of the wafer temperature may be inhibited andtemperature control characteristics are improved.

In addition, in the embodiment unit, the maximum temperature differencebetween the wafer surfaces during the heating step was several degrees.That is, it was found that the uniformity of the wafer temperaturebetween wafer surfaces (including during the process) may be remarkablyimproved.

In addition, the temperature difference between the central portion andthe peripheral portion of the wafer during the heating step wasincreased to 15° C. at most. However, the state continued only for 2 or3 minutes, so that the wafers were not affected badly thereby.

As described above, when the bottom heater 132 and the ceiling heater134 and the like are provided in addition to the side heater 130 as thesecond embodiment, the uniformity between wafer surface temperaturesduring the heating step and during the process may be greatly improved.

The above embodiments are explained for the annealing process to thecopper films. However, the thermal process is not limited unless itcauses a problem of metal contamination or the like. For example, in athermal process for vitrificating a resin layer as an interlayerdielectric film, the process temperature is about 300 to 600° C., and anNH₃ gas or the like is used as a process gas.

The object to be processed is not limited to the semiconductor wafer,but may be a glass substrate, a LCD substrate or the like.

1. A thermal processing unit comprising: a tubular processing container,an object-to-be-processed holding unit that holds a plurality of objectsto be processed in a tier-like manner and that can be inserted into andtaken out from the processing container, a process-gas introducing unitthat introduces a predetermined process gas into the processingcontainer, a heating unit provided in the processing container, theheating unit heating the plurality of objects to be processed held bythe object-to-be-processed holding unit when the object-to-be-processedholding unit is inserted into the processing container, and a containercooling unit that cools an outside wall surface of the processingcontainer, wherein a thermal-reflectivity lowering process for loweringthermal reflectivity of an inside wall surface of the processingcontainer has been conducted to the inside wall surface of theprocessing container.
 2. A thermal processing unit according to claim 1,wherein the container cooling unit has: a cooling pipe arranged so as tocome in contact with the outside wall surface of the processingcontainer, and a cooling-medium introducing unit that causes a coolingmedium to flow into the cooling pipe.
 3. A thermal processing unitaccording to claim 2, wherein the cooling pipe is wound around theoutside wall surface of the processing container.
 4. A thermalprocessing unit according to claim 2, wherein the cooling pipe has adouble-tube structure having an inner tube and an outer tube, and thecooling medium is caused to flow into a gap between the inner tube andthe outer tube.
 5. A thermal processing unit according to claim 2,wherein the outside wall surface of the processing container and thecooling pipe are coated with a heat-transfer material.
 6. A thermalprocessing unit according to claim 5, wherein the heat-transfer materialis a heat-transfer cement.
 7. A thermal processing unit according toclaim 1, further comprising a cooling-gas introducing unit thatintroduces a predetermined cooling gas into the processing containerwhen the objects to be processed are cooled.
 8. A thermal processingunit according to claim 1, wherein the heating unit has a side heaterextending in a vertical direction along the inside wall surface of theprocessing container.
 9. A thermal processing unit according to claim 8,wherein a upper portion of the side heater is supported by a ceilingportion of the processing container.
 10. A thermal processing unitaccording to claim 1, wherein the heating unit has a ceiling heaterarranged in a vicinity of a ceiling portion of theobject-to-be-processed holding unit inserted into the processingcontainer, the ceiling heater heating the ceiling portion.
 11. A thermalprocessing unit according to claim 10, wherein the ceiling heater issupported by a ceiling portion of the processing container.
 12. Athermal processing unit according to claim 1, wherein the heating unithas a bottom heater arranged in a vicinity of a bottom portion of theobject-to-be-processed holding unit inserted into the processingcontainer, the bottom heater heating the bottom portion.
 13. A thermalprocessing unit according to claim 12, wherein the processing containerhas a lower-end opening, the lower-end opening can be opened and closedby a lid member, and the bottom heater is supported by the lid member.14. A thermal processing unit according to claim 12, wherein the bottomheater is supported by a ceiling portion of the processing container.15. A thermal processing unit according to claim 1, wherein theprocessing container consists of quartz, stainless steel or aluminum.16. A thermal processing unit according to claim 1, wherein the objectsto be processed are heated to a range of 50 to 600° C.
 17. A thermalprocessing unit comprising: a tubular processing container, anobject-to-be-processed holding unit that holds a plurality of objects tobe processed in a tier-like manner and that can be inserted into andtaken out from the processing container, a process-gas introducing unitthat introduces a predetermined process gas into the processingcontainer, a heating unit provided in the processing container, theheating unit heating the plurality of objects to be processed held bythe object-to-be-processed holding unit when the object-to-be-processedholding unit is inserted into the processing container, and a containercooling unit that cools an outside wall surface of the processingcontainer, wherein the heating unit has a side heater extending in avertical direction along the inside wall surface of the processingcontainer, and wherein a lower portion of the side heater is supportedby a bottom portion of the processing container.